It seems to me that one of the advertisers in the headings here on the forum was for a company with design plans for house/barn type units that also had an RV in mind. Try as I might I can not find any bookmark anywhere in my system for the company. If I recall correctly they were just what you are looking for. I am sorry that I can not be of more help in tracking this down.
Did anyone else see the ad and take a look (and still have a pointer to the company)?
Only he who attempts the ridiculous can achieve the impossble.